Asynchronously using a synchronous disposable that returns a Promise

[rictic]

Should a promise returned by a Symbol.dispose method be awaited by AsyncDisposableStack#use / await using?

Put another way:

{
  const stack = new AsyncDisposableStack();
  const neverResolves = Promise.withResolvers().promise;
  stack.use({[Symbol.dispose]() { return neverResolves }});
  await stack.disposeAsync();
  console.log('[1] does this line of code ever run?'); 
}

{
  {
    const neverResolves = Promise.withResolvers().promise;
    await using _ = {[Symbol.dispose]: () => neverResolves};
  }
  console.log('[2] does this line of code ever run?');
}

[rictic]

The native implementation in Chrome Canary Version 135.0.7026.0 (Official Build) canary (arm64) does not run either console.log statement. [Edit: Version 135.0.7036.0 runs both log statements.]

The TypeScript runtime emit for the second code snippet does log. TypeScript Playground Link

The AsyncDisposableStack polyfill in https://github.com/es-shims/DisposableStack does log for the first snippet.

The AsyncDisposableStack polyfill at https://github.com/nberlette/dispose does not log for the first snippet.

[rictic]

My read of the spec is that both should be logged, because of https://tc39.es/proposal-explicit-resource-management/#sec-getdisposemethod 1.b.ii which says that GetDisposeMethod, when called with an async-dispose hint, should return a newly created closure that synchronously returns a new, already-settled promise when it's called. That promise is rejected if the Symbol.dispose method throws, the promise is resolved to undefined.

So even though CreateDisposableResource when called with an async-dispose hint always creates a DisposableResource Record with an async hint, the DisposeMethod it's given isn't able to observe any promise that might be returned by a Symbol.dispose method.

[rbuckton]

Both should be logged. Per https://arai-a.github.io/ecma262-compare/?pr=3000&id=sec-getdisposemethod, the result of invoking the Symbol.dispose method is only used to reject the Promise.

@syg: Sounds like a bug in V8?

[syg]

cc @rmahdav

[syg]

Confirm there's a bug in V8 with some accidental promise chaining in the async-from-sync adapter.

[rmahdav]

Thank you, Peter. A fix has landed for this bug.